Camera system with means for detecting the condition of back-up power supply

ABSTRACT

A camera with circuitry, a main power source for supplying electric power to the circuitry, a back-up power source for supplying electric power to the circuitry independently from the main power source, a detector for detecting the condition of the back-up power source to produce a warning signal when the back-up power source can not supply sufficient electric power to the circuitry, starting the operation of the detector when the main power source has recovered, setting data to the circuitry in accordance with a manual operation and interrupting the operation of the warning signal when the data setting is operated.

This application is a divisional application of application Ser. No.309,654, filed Feb. 13, 1989, now U.S. Pat. No. 4,947,203 which is adivisional application of application Ser. No. 220,066, filed July 15,1988, now U.S. Pat. No. 4,860,046 which is a divisional application ofapplication Ser. No. 043,758 filed Feb. 29, 1987, now U.S. Pat. No.4,763,144, which is a divisional application of application Ser. No.888,600, filed July 23, 1986, now U.S. Pat. No. 4,712,904, which in turnwas a divisional application of application Ser. No. 634,474, filed July25, 1984, now U.S. Pat. No. 4,621,914.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photographic camera capable offunctioning with stored data such as, for example, stored data of thefilm speed.

2. Description of the Prior Art

For the purpose of setting the film speed in a photographic camera, ithas been proposed to provide a surface of a film cartridge with a codepattern comprised of particular combinations of conductive andnon-conductive areas in correspondence with the film speed. When such afilm cartridge is loaded in the camera, a plurality of feelers providedin the camera detect such a particular combination of conductive andnon-conductive areas to set the film speed automatically in the camera.

SUMMARY OF THE INVENTION

The present invention improves the operation of a camera with respect toa back-up power source for operating the camera independently of themain power source.

A feature of the invention is the detection of the condition of theback-up power source to produce a warning signal when the detectionreveals that the back-up power source can not supply sufficient electricpower to the circuit means.

A further feature of the invention is the provision of means forstarting the operation of the detecting means when the main power sourcemeans has recovered.

Yet a further feature of the invention is the setting of data to thecircuit means in accordance with a manual operation and interrupting thewarning when the data setting means is operated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withthe preferred embodiments thereof in connection with the followingdrawings, in which:

FIG. 1 is a perspective view of a camera system according to a preferredembodiment of the present invention;

FIG. 2 is a diagrammatic view showing relationship between a loaded filmcartridge and feelers for reading data provided on the film cartridge;

FIG. 3 is a diagrammatic view showing a mechanism of a frame-numbercounter;

FIGS. 4a and 4b, taken together as shown in FIG. 4, show a circuitdiagram employed in the camera system of FIG. 1;

FIG. 5 is a circuit diagram showing a detail of the circuit CIM of FIG.4a;

FIG. 6 is a circuit diagram showing a detail of a circuit CAD and acircuit EM of FIG. 4a;

FIG. 7 is a flow chart of a microcomputer provided in the camera body,particularly showing the operations for the initial setting;

FIG. 8 is a flow chart particularly showing the operation when the backlid is closed;

FIG. 9 is a flow chart showing the detailed steps for step #4 of FIG. 7or #8 of FIG. 8;

FIG. 10 is a flow chart showing the detailed steps for step #7 of FIG. 7or #10 of FIG. 8;

FIGS. 11a to 11h show a flow chart for the camera control under variousoperating modes;

FIG. 12 is a circuit diagram showing the details of a display controlDPC of FIG. 4b;

FIG. 13 is a flow chart similar to FIG. 7, but showing a modificationthereof; and

FIGS. 14a and 14b are plan views of a display employed in the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENT

The present invention will now be described in connection with apreferred embodiment thereof with reference to the accompanyingdrawings.

Referring first to FIG. 1, a camera body 1 is shown as having a releasebutton 2 which actuates a light measuring switch (not shown) forperforming a light measurement when it is depressed halfway and actuatesa release switch (not shown) when it is depressed fully for actuating ashutter.

Reference numeral 3 represents a mode change-over switch employed in theform of a slide switch, movable to P, S, M and A positions: the Pposition represents a programmed mode; the S position represents anexposure time priority mode in which the aperture is automaticallycontrolled; the M position represents a manual mode; and the A positionrepresents an aperture priority mode in which the exposure time isautomatically controlled. Reference numeral 4 represents a displaysection for displaying a control exposure time, an aperture value, afilm sensitivity, and override data. An example of the display is shownin FIG. 14.

Reference numeral 5 represents an aperture value setting key, referencenumeral 6 represents a shutter speed setting key, and reference numerals7 and 8 respectively represent up-shift and down-shift keys for changingthe value of a selected item, such as aperture value F or shutter speedSS. A counter display window 9 displays the number of film framesphotographed.

Reference numeral 10 represents an ISO mode key. When this ISO mode key10 is depressed, ISO data utilized in the camera body 1 are displayed onthe display section 4 and can be changed at any time by means of theup-shift and down-shift keys 7 and 8.

Reference numeral 11 represents an override key. When this override key11 is depressed, override data are displayed on the display section 4and can be changed at any time by the manipulation of the up-shift anddown-shift keys 7 and 8. Reference numeral 13 represents a filminformation display window provided in a back cover 13 of the camerabody 1.

Within the camera body 1 shown in FIG. 1, there is provided, as shown inFIG. 2, code read-out feelers 15 and 16 for reading the ISO dataprovided on a film cartridge 14. These feelers 15 and 16 have aplurality of feeler pieces AT2-AT6, FT8, FT9, FT10, RT11, and RT12 (FIG.6) adapted to contact code electrodes K1 to K10 formed on the outerperipheral surface of the film cartridge 14, for example, in a matrix ofsix rows and two columns.

Each of these feeler pieces AT2 to RT12 are fixed by means of vices to apost 18 made of an insulating material and planted within the camerabody 1.

As shown in FIG. 3, within the camera body 1, there is provided aback-lid detecting switch 31 adapted to be opened and closed when a backlid 33 of the camera is closed and opened, respectively, and a counterswitch 32 associated with a film counter 34. The counter switch 32 isselectively closed and opened by a lever 36, driven by a cam 35, and isclosed when the count of the film counter shows a value within the rangeof S to 1 and it is opened when it shows a value more than 1.

FIG. 4a illustrates a circuit diagram of the entire camera systemembodying the present invention. Reference character PO1 represents apower-on reset circuit provided with a battery power source BAB andadapted to output a power-on reset signal from a terminal PR1 when thesupply of electric power from a power line VC is re-initiated.

Reference character MCB represents a microcomputer for controlling theoperation of the entire camera system. The operation of thismicrocomputer MCB is shown in the flow charts of FIGS. 7 to 10 and FIGS.11a to 11h. Reference numeral S1 represents a light measuring switchadapted to be closed upon the halfway depression of the release button2. Reference character ISS represents a switch adapted to be closed uponthe depression of the ISO mode key, and reference character ORSrepresents a switch adapted to be closed upon the depression of theoverride key 11. Reference characters FSS and SSS represent respectiveswitches adapted to be closed upon the depression of the aperture valuesetting key 5 and the exposure time key 6. Reference characters UPS andDOS represent switches adapted to be closed upon the depression of theup-shift key 7 and the down-shift key 8, respectively. Reference numeralRES represents a switch adapted to be closed upon the depression of arecall button 12. These switches are constituted in a key-matrix withoutput terminals O2, O3 and O4 and input terminals i1, i2 and i3 ofmicrocomputer MCB, and the one(s) which is(are) closed can be determinedby microcomputer MCB.

Microcomputer MCB is such that, when it is not operated, outputterminals O2, O3 and O4 are "High" and a line connected to inputterminal i1 is input to an interruption terminal itA through an ANDcircuit AN1, an OR circuit OR1, and AND circuit AN3. Accordingly, whenone of the light measuring switch S1, the ISO switch ISS and theoverride switch ORS is closed, interruption is effected to terminal itAand microcomputer MCB is then started.

Reference character BMS represents a main switch. When this main switchBMS is opened, an inverter IN2 produces a "Low" output, thereby placingthe microcomputer in an inoperative condition. Furthermore, AND circuitAN3 is held in a disabled state and no interruption signal is input toterminal itA, with the microcomputer consequently not started. Inaddition, when battery BAB is removed to provide no power supply to lineVC, AND circuit AN3 is again held in a disabled state, thereby effectingno interruption. Accordingly, when battery BAB is not loaded or whenmain switch BMB is opened, microcomputer MCB remains inoperative.

Switch S2 is a switch adapted to be closed upon the full depression ofrelease button 2. When this release button switch S2 closes, inverterIN3 produces a "High" output and an interruption signal is input toterminal itA through AND circuit AN2, OR circuit OR1 and AND circuitAN3. When this interruption signal is input, and when a shutter chargeis completed and the calculation of exposure control data is alsocompleted, an exposure control operation is immediately carried out. Itis, however, to be noted that, so long as the microcomputer is carryingout a data exchange with other circuits, OR circuit OR3 produces a"High" output, causing AND circuit AN2 to be disabled. Thus, theinterruption by release button switch S2 will not take place.

A switch RCS is a back lid switch (corresponding to switch 31 in FIG. 3)adapted to be opened and closed when the camera back lid 33 is openedand closed, respectively. Accordingly, when the back lid is closed, theoutput of an inverter IN4 becomes "High" and a pulse is output from aone-shot circuit OS1 to set a flip-flop RF1, with an interruption signalconsequently input to a terminal itB. Then, microcomputer MCB performsan operation which is to be performed when the back lid is closed. Afterthis operation has been performed, a pulse is output from a terminal O18to reset flip-flop RF1 thereby establishing the inoperative condition ofmicrocomputer MCB.

Reference character LE represents an interchangeable lens assembly whichis electrically connected to the camera body through connectors CNF andCNB1 so that fixed data stored in a circuit LEC inside the lensassembly, such as an aperture value, can be serially applied tomicrocomputer MCB through an interface circuit BOL (FIG. 4a). Thisoperation causes microcomputer MCB to produce a "High" output fromterminal O5. Then, when a serial-in and serial-out command are executed,eight clock pulses are output from a serial clock pulse terminal SCP. Insynchronism with these clock pulses, data from the lens assembly LE areinput and are read in from a serial input terminal SIN. By repeatingthis serial input command a number of times, necessary data from thelens LE can be all read in.

Reference character CAD represents a code pattern circuit for outputtingdata of the code pattern provided on the film cartridge 14. Referencecharacter EM represents a code plate for outputing data corresponding toa selected exposure control mode, and reference character SFC representsa counter switch (corresponding to that shown by 32 in FIG. 3) adaptedto be closed when the film counter is in a preparatory winding position,but opened when it is in a photo-taking position.

Reference numeral BUB represents a back-up battery in FIG. 4a. Referencecharacter CIM is a circuit for storing the ISO data, and for readingdata CAD from the film cartridge, mode data and a signal from the filmcounter switch SFC, the details of which are shown in FIG. 5. Thiscircuit CIM is powered by the back-up battery BUB through a diode D21and is also powered by the main battery BAB through diode D20. Referencecharacter BCC represents a circuit for checking the output voltage ofthe back-up battery BUB and is powered by a power line VB through atransistor BTO such that, when the output of the back-up battery BUB ishigher than a predetermined value, BCC generates a "High" signal to aterminal i20. Reference character PO5 represents a power-on resetcircuit capable of outputing a reset signal when the back-up battery isloaded. The reset signal is fed only to an ISO data storage registerwithin the circuit CIM, the content of that register being reset onlywhen the back-up battery BUB is loaded. Terminals O30, O31, O32 areterminals for producing signals that control the operating mode of thecircuit CIM. In the circuit CIM, an operation corresponding to outputfrom these terminals takes place. An OR circuit OR50 receives signalsfrom these terminals O30, O31 and O32, and its output terminal isconnected to one input terminal of OR circuit OR3. Accordingly, whendata transmission is effected between circuit CIM and microcomputer MCB,interruption to terminal itA by release switch S2 is inhibited.

Referring to FIG. 5, reference character SD1 represents a circuit forreading, in synchronism with the clock pulses from a terminal SCP, datawhich are serially input from a terminal SOU of microcomputer MCB. Acounter LPC which operates when terminal O30 is "High", counts thenumber of synchronizing clock pulses and outputs a latch pulse when ithas counted eight clock pulses. This latch pulse is fed to a registerLAC and, when this pulse is input, data from the reading circuit SD1 arelatched. Register LAC is adapted to be reset by a pulse fed from thepower-on reset circuit PO5 shown in FIG. 5.

Reference character DSC represents a data selector. Its operation issuch that, when the signal from terminals O31 and O32 is "01", ISO datastored in the register LAC, as applied to an input section d1 isproduced. When the signal from terminals O31 and O32 is "10", the dataon the film container as applied to an input section d2 is produced.When the signal from terminals O31 and O32 is "11", the datarepresentative of the selective mode and the counter switch as appliedto an input section d3 are produced. Also, when the signal fromterminals O31 and O32 is "00", the data selector DSC produces no data. Aserial data output circuit SDO sequentially, serially outputs, when theoutput of an OR circuit OR52 becomes "High", data from the data selectorDSC to terminal SIN on the basis of the synchronizing clock pulses.

The details of each of CAD and EM are shown in FIG. 6. Referring now toFIG. 6, the film cartridge 14 is provided with code patterns K1 to K12.Portions K1 and K7 are always formed with electrically conductivematerial regardless of the type of film cartridge and, in theillustrated embodiment, an electrode COT connected to the groundcontacts them. Portions K2 to K6 are provided with conductive andnon-conductive patterns according to the data corresponding to the ISOsensitivity of a film within the film cartridge 14, an example of whichis shown in Table 1.

Contact pieces AT2 to AT6 contact portions K2 to K6, respectively, andare connected to input terminal d2 of data selector DSC, shown in FIG.5, through pull-up resistors and inverters. Portions K8 to K10 areprovided with code patterns corresponding to the data of the number offrames of the film contained in the film cartridge 14. Although contactpieces FT8, FT9 and FT10 contact these portions, data from these contactpieces are not input anywhere because, in the illustrated embodiment,these data are not utilized.

Portions K11 and K12 are provided with exposure range data.

Contact pieces RT11 and RT12 contact these portions K11 and K12 forsupplying data on portions K11 and K12 to input terminal d2 of dataselector DSC through pull-up resistors and inverters.

Reference characters MT1, MT2 and CMT represent data output code platesfor producing data which represents various exposure calculation modes.A slide member VT is moved in accordance with the movement of the modechangeover switch 3. When slide member VT is moved to the P positionrepresenting the programmed mode, data "00" are applied to inputterminal d2 of data selector DSC. When slide member VT is moved to the Sposition representing the exposure time priority mode (hereinafterreferred to as S mode), data "01" are applied to input terminal d2. Whenslide member VT is moved to the A position representing the aperturepriority mode (hereinafter referred to as A mode), data "10" are appliedto input terminal d2. When slide member VT is moved to the M positionrepresenting the manual mode, data "11" are applied to input terminald2. In addition to these data, a signal from film counter switch SFCthrough an inverter IN5 is also applied to input terminal d2 of dataselector DSC.

Referring back to FIG. 4b, reference character FL represents a flashdevice in which a power source battery BAF, a firing and control circuitFLC and a main switch FMS are incorporated. Flash device FL is providedwith a connector CNF which, when flash device FL is mounted on thecamera body, is electrically connected with a connector CNB2 foreffecting signal transmission between the flash device and a controlcircuit FCC so as to control the flash device.

Reference character LMC represents a light measuring circuit. The resultof the light measuring as effected by light measuring circuit LMC isapplied to an analog input terminal ANI of the microcomputer. Themicrocomputer also receives a reference potential for thedigital-to-analog conversion at its terminal VR1. Reference characterDPC represents a display circuit operable to drive both a liquid crystaldisplay section LDP for the data display and a light emitting diode FLDfor the display of flash photography. Display circuit DPC receivesdisplay data from a terminal SOU during a period in which the output ofa terminal O10 is "High" and effects the display based on this data. Thedetails of the display section will be described later in connectionwith FIG. 12. Reference character RLC represents a release circuit whichreleases the engagement of an exposure control mechanism based on apulse from a terminal O12.

Reference character APC represents an aperture control circuit operableto read data of the number of f-stop positions to be stopped down, whichare fed from terminal SOU during a period in which a terminal O13 is"High", and to interrupt the stopping-down of the aperture of the camerato determine the aperture opening when the data so read coincides withthe number of f-stop positions actually stopped down. Referencecharacter TIC represents an exposure time control circuit operable toread exposure time control data output from terminal SOU during a periodin which a terminal O14 is "High" and to initiate a shutter closingoperation after a time corresponding to the data so read has passedsince the closure of the count switch S3. Furthermore, a terminal TIEbecomes "High" when a release signal RLS is output, and becomes "Low"after a predetermined time, for example, 50 milliseconds, has passedsubsequent to the initiation of the shutter closing operation.

With reference to the flow chart shown in FIG. 7, and FIG. 4a theoperation of this system will now be described. When the power isinitiated from a terminal VC, the microcomputer MCB is activated andperforms an initial resetting operation. Also, by the power-on resetsignal PR1, the flip-flop RF1 is reset and the display circuit DPCactuated by power from terminal VC is also reset.

Microcomputer MCB produces "High" signals from terminals O1 to O4 and"Low" signals from terminals O5 to O18 at step #0. In addition, itproduces a "High" at terminal O31 a "Low" from terminals O30 and O32 toperform the serial input and output operation. Thereupon, the data onthe film cartridge from detector CAD are read in register IOR throughcircuit CIM which data are in turn set in a register CAR. The method ofsetting the data in register CAR is shown in Table 3 at the end of thespecification.

Subsequently, when microcomputer MCB produces "High" signals from itsoutput terminal O32, the serial input and output reading is performed,thereby serially reading the ISO data stored in a register LAC. The ISOdata so read out are then set in a register MER. Then, a decision ismade in order to determine if input terminal i20 is "High". If it is"High", it means that the output voltage of the back-up battery BUB issufficient. Then, a further decision is made to determine if the dataread out from the register LAC are normal. This decision is such that,unless all of the bits are "0", the data so read out are determinednormal. Thus, if the back-up battery is normal and the data from theregister LAC are normal, data MER read out from the register LAC are setin a register SVR and interruption to terminals itA and itB is enabledwith the program flow proceeding to step #3.

However, if the output voltage of the back-up battery BUB is determinedlower than the predetermined value at step #1, or if the result of thedetermination at step #2 indicates that the normal data are not read outfrom the register LAC, the program flow proceeds to step #4. At step #4,a decision is made in order to determine, by examining the contents ofregister CAR, whether the data from the film cartridge are read in. Ifthe result of the determination is yes, that ISO data based on the datafrom the film cartridge are set in the register SVR, and if it is no,fixed data (for example, ISO 100 Sv=5) are set in the register SVR.Then, the contents of the register SVR are set in an input/outputregister IOR. Then, terminal O30 is "High" and, thereafter, the serialinput and output reading is performed. Thus, the contents of theregister SVR are transferred to a storage register LAC. Subsequently,bits MDR0 and MDR7 are set to be "1" and the remaining bits are set tobe "0". Register MDR is the register in which data indicative of displaymethods are set, the weight of each bit being as follows.

A bit MDR0 is "0" when neither a symbol ISO nor a symbol SS isdisplayed, but becomes "1" when the symbol ISO or SS is displayed. MDR1is "1" when the exposure time is to be displayed at the display section,but becomes "0" when the ISO data is displayed. MDR2 and MDR3 are "01"and "10" if override data are on a "+ side" and a "- side",respectively, when the override data is to be displayed. When theoverride data is 0 and are to be displayed, MDR2 and MDR3 become "11".But, they become "00" when no override data is displayed. Accordingly,when MDR2 and MDR3 are "00", no display concerning the override iseffected. When they are "01", a symbol "+/-" of the override isdisplayed together with "+" preceding the override data; when they are"01", the symbol "+/-" is displayed together with "-" preceding theoverride data; and when they are "11", the symbol "+/-" is displayedand, at this time, the displayed override data, which is 0, is appliedwith neither "+" nor "-" preceding such a display "0". It is to be notedthat, if MDR2 and MDR3 are "01" and "10", the symbol "+/-" will bedisplayed even when an exposure control value is displayed.

MDR4 is "1" when an F-value is to be displayed and when "0" it is notdisplayed. Accordingly, when it is "1", "F" is displayed, but when it is"0", "F" is not displayed. MDR5 and MDR6 are set with a symbolrepresentative of a display manner of the light emitting diode FLD whichindicates the state of the flash device. When it is "00", the flashdevice is not mounted on the camera and the light emitting diode is notlit. When it is "01", it indicates that the flash device is mounted onthe camera body and is powered and the blinking takes place at thefrequency of 2 Hz. When it is "10", it indicates that the charging ofthe flash device is completed with the light emitting diode being lit.When it is "11", it indicates the completion of the light adjustmentand, in this case, the light emitting diode FLD blinks at the frequencyof 8 Hz. MDR7 permits the entire liquid crystal display unit to blink at2 Hz when it is "1", but it is lit continuously when it is "0".

Then, the contents of the register SVR, blank display data BLD and thecontents of the register MDR are transferred to the display section DPCand, at the same time, the terminals O1, O2 and O4 are "Low" to enablethe interruption of signals to the terminals itA and itB, and tenseconds is allowed to pass. Accordingly, when the contents of thestorage circuit LAC powered by the back-up battery BUB vanish or whenthe output of the back-up battery BUB is not normal on the occasion whenthe power source battery BAB for the microcomputer is loaded, the ISOdata based on the data on the film cartridge or the fixed ISO data isset, and these data are displayed blinking for ten seconds as a warning.Moreover, since the terminals O2 and O4 are "Low", an interruptionsignal can be applied to terminal itA only when the ISO switch ISS isclosed. Accordingly, no exposure control operation is initiated evenwhen the release button is manipulated. In other words, the shuttermechanism is held in a release-locked condition. In order to escape fromthis condition, the ISO switch should be manipulated or ten secondsshould be allowed to pass.

After the passage of ten seconds, the terminals O2 and O4 are "High" andterminal O1 is "Low" at step #3, and thereafter, data necessary to turnon the display are fed to the display section DPC and a "HALT" conditionis then resumed. However, it is to be noted that, when the normal ISOdata is read out from the register LAC, this data is set and the programflow immediately proceeds to step #3 with no display consequently takingplace.

FIG. 8 illustrates the operation that takes place when the interruptionsignal is input to terminal itB as a result of the closure of the backcover. At first, a predetermined time (for example, 0.5 sec.) is allowedto pass after the closure of the back cover. This is because, shortlyafter the back cover has been closed, the film cartridge may undergo avibratory motion and, therefore, the contact of the feelers 15 and 16with the film cartridge may not be stabilized. Then, terminals O2, O3and O4 are "High" and terminals O1, O5 to O18, O30 and O32 are "Low".Furthermore, terminal O31 is "High", and then the serial input andoutput reading is performed. Accordingly, data are read out from thefilm cartridge. Subsequently, based on the read data, a decision is madein order to determine if the data is provided on the film cartridge. Ifthe data are provided on the film cartridge, the ISO data based on thisdata is set in the register SVR, but if it is not provided, the contentsof the register SVR remain unchanged.

Thereafter, by rendering the bit MDR0 to be "1" and the remaining bitsMDR1 to MDR7 to be "0", the contents of the register SVR, the blank dataBLD and the contents of the register MDR are transferred to the displaysection DPC, thereby displaying the set ISO data. Then, terminal O18produces a pulse with which the flip-flop RF1 is reset. Then, terminalsitA and itB are enabled to receive interruption signals within the nextfive seconds. After the lapse of the five seconds, the display is turnedoff with the "HALT" condition established in a manner similar to thateffected at step #3.

The details of detection of the presence of CAR at steps #4 or #8 willnow be described with reference to FIG. 9. As shown in Table 1 (at theend of the specification), in the case of the film cartridge providedwith the code pattern, at least one of the portions K6 and K5 is aconductive portion. If "1" is read in either one of the bits CAR4 andCAR3 of the register CAR, the film cartridge loaded is regarded ashaving the code pattern, and therefore, the setting of the data from thecode pattern is carried out. However, if both of the bits are "0", itmeans that the film cartridge having no code pattern is loaded or thatno film cartridge is loaded and, in that case, no setting of the databased on the contents of the register is carried out.

The details of the film sensitivity setting operation at steps #7 or #10will be hereinafter described in connection with FIG. 10. At first, 16His set in the register SVR, wherein H represents a hexademical numbersystem.

Each of the registers SVR1 and SVR2 has 8 bits, each bit being weighted16, 8, 4, 2, 1, 1/2, 1/4 and 1/8 from the most significant bit. The filmsensitivity is variable by a unit of 1/3 Ev in terms of the APEX value.If a fraction portion of the film sensitivity of the film loaded in thecamera is 1/3 or 2/3, it is approximated to 1/4 or 3/4 (=1/4+1/2),respectively. Accordingly, 16H set in the register SVR at step #1corresponds to Sv=22/3.

Then, if bits CAR4 and CAR5 of the register CAR are "11", 08H, is addedto the contents of the register SVR1. Similarly, if CAR4 and CAR5 are"10", 04H is added, and if they are "01", 02H is added. Accordingly, ifthe bits of the fraction portion are "11", Sv=1 is added to give 1EHwith the fraction portion being 3/4. However, if the bits of thefraction portion are "10", Sv=1/2 is added to give 1AH with the fractionportion being 1/4. Furthermore, if the bits are "01", Sv=1/4 is added togive 18H with the fraction portion being 0.

Subsequently, if the bit CAR2 of the register CAR is 1, Sv=4 is added tothe contents of the register SVR1. Similarly, if the bit CAR1 of theregister CAR is 1, Sv=2 is added, and if the bit CAR0 is 1, Sv=1 isadded.

The foregoing operation will now be described in connection with thecase in which the film cartridge with ISO400 film is loaded in thecamera. In this case, as shown in Table 1, the portions K4 and K5 areconductive. In the register CAR, the bits CAR3 and CAR2 are "1" whilethe bits CAR4, CAR1 and CAR0 are "0". Then, 22H is added to the registerSVR to give 38H. This data will become 4+2+1=7 according to theweighting system of each bit, which corresponds to the APEX value Sv=7at ISO400.

The operation of the circuit shown in FIG. 4a will now be described inconnection with the flow charts of FIGS. 11a to 11h. When one of lightmeasuring switches S1, ISO switch ISS, and override switch ORS isclosed, provided that the power source battery BAB is loaded with themain switch BMS being closed, the interruption signal is applied toterminal itA through the AND circuit AN3 to initiate the operationstarting from step #1. At first, a decision is made in order todetermine if the content of a flag CCF is "1". This flag CCF will carry"1" when the data for the exposure control is calculated, or will carry"0" when it is not calculated. The operation which will take place whenthe interruption signal is input to terminal itA while the exposurecontrol value has been calculated will be described later.

When the flag CCF is "0", terminal O1 is "High". Thereupon, a transistorBTO is brought into a conductive state, thereby supplying electric powerfrom the line VB. Also, the AND circuit AN1 is disabled, and the ANDcircuit AN2 is enabled. Accordingly, a signal from the release switch S2can be applied to terminal itA as an interruption signal. Then,terminals O3 and O4 are "Low", and terminal O2 is "High", therebydetecting whether terminal i1 is "High" or not. If terminal i1 is"High", interruption takes place as a result of the closure of the lightmeasuring switch S1 and a flag LMF is therefore set to "1" and, at thesame time, terminal O2 is "Low". If the switch S1 is held open, and ifit is detected at step #13 that terminal i1 is "Low", only terminal O3is "High". Then, it is determined whether or not terminal i1 is "High".If it is detected as being "High", meaning that the interruption hastaken place as a result of the closure of the ISO switch ISS, a flag ISFis set with "1". However, if terminal i1 is "Low", meaning that theinterruption has taken place as a result of the closure of the overrideswitch ORS, a flag ORF is set with "1". Thereafter, terminal O3 is "Low"with the program proceeding to step #14.

At step #14, terminal O5 is "High". Then, by repeating the serial inputand output operation for a predetermined number of times, the data fromthe lens assembly LE are read in and the data so read in aresequentially stored in the register LDR. After this operation, terminalO5 is "Low" and terminal O31 and P32 are "High". Thereafter, the serialinput and output reading is performed to transfer the mode signal,applied from the code plate EM, and the signal from the counter switchSFC to register MOR. Thereafter, the terminals O31 and O32 are "Low". Itis to be noted that the data representing the mode is set in the bitsMOR0 and MOR1 while the signal from the counter switch SFC is set in thebit MOR2. In this way, both the condition of the film counter and asignal indicative of the exposure control mode are stored in theregister MOR.

Next, when terminal O9 is "High", a pulse having a pulse width of 50microsecond is output from terminal O8. Then, when data "00H" has beenset in the input/output register IOR, the serial input and outputoperation is performed. Upon this operation, the data from the flashdevice FL is loaded in the register IOR, which is in turn stored in theregister FDR. Step #15 is performed after terminal O9 is "Low".

At step #15, a signal obtained from the light measuring circuit LMC,indicating the result of measurement of a target object to bephotographed, is subjected to the analog-to-digital conversion.Thereafter, in order to eliminate, on the basis of the data from thelens assembly LE, terms of the full aperture value Avo and the fullaperture metering error Avc both included in the analog-to-digitalconverted data, the equation

    (Bv-Avo-Avc)+Avo+Avc=Bv

is calculated to give a data of the brightness of the target object.Thereupon, the following equation

    Bv+(SVR)=Ev

is calculated to given the exposure value Ev.

Then, a decision is made to determine if the bits MDR2 and MDR3 of theregister MDR are "01". If they are "01", it means the override on the"+" side as hereinbefore described and, therefore, the contents of aregister ORR1 in which the override data on the "+" side is set issubtracted from the exposure value Ev to give an Ev value. However, ifthe contents of MDR2 and MDR3 are not "01", a decision is subsequentlymade of the override on the "-" side and, therefore, the contents of aregister ORR2 in which the override data on the "-" side is added to theexposure value Ev to give an Ev value.

Upon completion of the foregoing operation, the program flow proceeds tostep #16 at which a calculating operation of the exposure control datatakes place. At first, at step #16, a decision is made in order todetermine if the P mode has been established. If the P mode has beenestablished, a calculation for the photo-taking in the P mode with theuse of an ambient light and a calculation for the photo-taking in the Pmode with the use of a flash light are performed, and a flag DCF1 is setto "0", followed by step #18. The flag DCF1 is a flag which will carry"1", when the present aperture value or the present exposure time ischanged, but will carry "0" when none of these is changed. In the Pmode, since any change of the aperture value or the exposure time willnot be accepted, the flag DCF1 is always "0".

If the result of the decision at step #16 indicates that it is not the Pmode, the program flow proceeds to step #19 at which another decision ismade to find if it is the A mode. If it shows that it is the A mode, achange in the present aperture value is accepted and for this purpose,the operation is performed to effect such change of the data. At first,terminal O2 is "High" and a decision is then made to find if terminal i2is "High". If terminal i2 is "High", the aperture setting switch FSS isto be closed. Then, a decision is made to find if terminal i3 is "High".If terminal i3 is "High", the up-shift switch UPS is to be closed. Inthis case, terminal O2 is "Low", and the operation is performed tochange the data in a direction towards a smaller aperture. That is, adecision is first made to find if the contents of a register AVR3 inwhich the preset aperture value data is set is on the side of a largeraperture than the full aperture value data Avo fed from the ROM of thelens assembly LE. If the result of the decision is yes (which occurswhen the lens assembly is interchanged), the contents of the registerAVR3 is set to Avo with the program flow subsequently proceeding to step#20. However, if the result of the decision is no, that is, if thecontents of the register AVR3 is not on the side of a larger aperturethan Avo, another decision is made to find if it is equal to Avo. A datadAv from the lens assembly LE, if the contents of register AVR3 areequal to Avo, or 1/2 if it is not equal thereto, is added to thecontents of the register AVR3 and a decision is then made to find if thecontents of the register is of a value greater than the maximum aperturevalue data Avm from the lens assembly. If it is of a greater value, themaximum aperture value Avm is set in the register AVR3 and the programflow proceeds to step #20, but if it is not of a greater value, step #20immediately takes place. The maximum aperture value data Avm is also fedfrom the lens ROM.

The data dAv will now be described. The full aperture value Avo takes adifferent value when the type of the interchangeable lens assembly ischanged. Some interchangeable lens assemblies have the full aperturevalue Avo which can be divided by 0.5 Ev, i.e., in a unit of 0.5 Ev(Avo=0.5, 0.1, 1.5 2.0 . . . ), and others not in a unit of 0.5 Ev (forexample, F2.5(Av=2.64), F3.5(Av=3.61), F1.8(Av=1.7) and so on). In thecamera body, however, the aperture value to be set is in the multiple of0.5 Ev, except for the fully opened aperture value. Therefore, in thecase where the fully opened aperture is not in the multiple of 0.5 Ev,the first stop-down change from the fully opened aperture value to thenext aperture value results in a change dAv which is smaller than 0.5Ev. Therefore, after the first stop-down change, the aperture value canbe set to the multiple of 0.5 Ev, with the aperture change effected atthe rate of 0.5 Ev. Accordingly, in the case of the F2.5 lens assembly,dAv=0.36; in the case of the F3.5 lens assembly, dAv=0.39; and in thecase of the F1.8 lens assembly, dAv=0.3. This data dAv is alsotransferred to the camera body from the lens ROM.

If it is determined that terminal i3 is not "High" and, at the sametime, the up-shift switch UPS is not closed at the timing when terminalO2 is "High", terminal O2 is "Low", and terminal O3 is "High", therebymaking a detection, based on the state of terminal i3, whether or notthe down-shift switch is closed. If the down-shift switch DOS is closed,terminal O3 is "Low" and 1/2 is subtracted from the content of theregister AVR3. Then, a decision is made to find if the result of thesubtraction is on the side of the fully opened aperture with respect tothe fully opened aperture value Avo, if it is of a value on the side ofthe fully opened aperture, the fully opened aperture value Avo is set inthe register AVR3 with the program flow subsequently proceeding to step#20.

At step #20, the flag DCF1 is set to "1" to show that the setting datahas been changed, followed by step #21. However, in the case where theaperture switch FSS is not closed, or where both the up-shift anddown-shift switches UPS and DOS are not closed, the data will not bechanged and the flag DCF1 is set to "0" at step #23, followed by step#21. At step #21, the calculation for the photo-taking under the A modewith the use of the ambient light is performed and, at the subsequentstep #22, the calculation for the photo-taking under the A mode with theuse of the flash light is performed. Thereafter, the program flowproceeds to step #24.

If it is determined that the mode is other than the A mode at step #19,a decision is made at step #25 to determine if it is the S mode. If itis determined as the S mode, a decision is made at steps #25 and #26 todetermine from the state of terminal i2 if the exposure time switch SSSis closed. If the result shows that the exposure time switch SSS is notclosed, the flag DCF1 is set to "0" at step #28 followed by step #29.However, if the result of decision at step #27 shows that the exposuretime switch SSS is closed, a decision is then made to find if theup-shift switch UPS is closed. If the result of the decision at step #30shows that the up-shift switch UPS is closed, "1" is added to thecontent of the register TVR3 in which the present exposure time data isset. Whether or not the result of the addition is greater than the dataTvm is determined at step #31. If the result of the addition is greaterthan the data Tvm, Tvm is set in the register TVR3, but if it is notgreater than that, the content remains unchanged and the flag DCF1 isset to "1" at step #32, followed by step #29.

If the result of the decision at step #30 shows that the up-shift switchUPS is not closed, whether or not the down-shift switch DOS is closed isdetermined at step #33. If the down-shift DOS is closed, "1" issubtracted from the register TVR3 at step #34, and subsequently, adecision is made to determine if the result of the subtraction has alonger exposure time than the maximum exposure time Tvo. If it has thelonger exposure time, Tvo is set in the register TVR3, but if not, thecontent remains unchanged and the flag DCF1 is set to "1". The programflow then proceeding to step #29.

When the exposure time switch SSS is not closed, or when both of theup-shift and the down-shift switches UPS and DOS are closed while theexposure time switch SSS is closed, the flag DCF1 is set to "0" and theprogram flow proceeds to step #29. At step #29, the calculation for thephoto-taking under the S mode with the use of the ambient light isperformed, followed by the calculation for the photo-taking under the Smode with the use of the flash light. Then, the program flowsubsequently proceeds to step #18.

If it is determined at step #25 that the mode is not the S mode, themode is the M mode. In that case, both the aperture value data and theexposure time value data can be changed. When both of the aperture valuedata and the exposure time data have been changed in a manner similar tothat described hereinbefore, the calculation for the photo-taking underthe M mode with the use of the ambient light and that with the use ofthe flash light are successively performed. Thereafter, the program flowproceeds to step #18.

At step #18, since the exposure control data has been calculated, theexposure control operation can be carried out and thus, flag CCF is setto "1". Then, the interruption signal can be input to terminal itA oritB at any time. Subsequently, a decision is made based on the data fromthe flash device FL in order to find if the flash device being poweredis loaded. If no loading signal is present, indicating that the flashdevice is not loaded, the bits MDR5 and MDR6 of the register MDR aremade to be "00", and the program flow proceeds to step #35. If, however,the loading signal is present, a decision is then made to find if asignal indicative of the completion of the light adjustment, whichsignal is hereinafter referred to as FDC signal, is being input. If theFDC signal is input, the bits MDR5 and MDR6 of the register MDR are setto "11" with the program flow then proceeding to step #35. However, ifthe FCD signal is not input, a decision is then made to determine if acharge completion signal is being input. If the charge completion signalis input, bits MDR5 and MDR6 are set to "10", but if not, they are setto "01".

At step #35, terminal O9 is "High" and, thereafter, the transfer of datafrom the camera to the flash device FL takes place. At the subsequentstep #36, a pulse having a pulse width of 100 microseconds is producedfrom terminal O8. Then, the ISO data set in the register SVR is set inthe input/output register IOR, the content of which is output through adigital-to-analog converter from an analog signal output terminal AN0.Thereupon, by performing the serial input and output operation, the ISOdata is transferred to the flash device. Following that, the content ofthe register AVR2 in which the aperture value data is loaded for theflash photography is loaded in the register IOR and is then transferredto the flash device and, at the same time, the content of the registerTVR2 in which is set the exposure time data for the flash photography isset in the register IOR and is then transferred to the flash device.Thereafter, of the data from the lens assembly LE, the content of aregister LDRf in which a focal length data is set is loaded in theregister IOR and is then transferred to the flash device FL, therebyproducing a "Low" signal from terminal O9. In this way, the data fromthe camera body are transmitted to the flash device. Based on the dataso transferred, the flash device performs various functions includingthe display of the available range and the automatic setting of thelighting coverage angle.

At step #40, a decision is made as to whether the flag ISF is "1". Whenit is "1" meaning that the ISO switch is closed, the program goes tostep #43. However, when it is "0", a decision is made at step #41 inorder to determine if the flag ORF is "1". If it is "1", indicating theclosure of the override switch ORS, the program flow proceeds to step#44. However, if it is "0", the content of a bit MOR2 of register MOR isdetermined. If the content of the bit MOR2 is "0", it indicates that thefilm count switch SFC is closed, but the film counter has not yetreached the position 1 (the first frame number that can be photographed)and, therefore, the program flow proceeds to step #52. If at step #42,it is determined that bit MOR2 of register MOR is "1" meaning that thefilm counter switch SFC is opened, the program flow proceeds to step#46. At this time, since it is under the mode in which the exposurecontrol value is to be displayed, bits MDR2 and MDR3 are made to be "00"if they are "11", and at the same time, bits MDR1 and MDR4 are renderedto be "1". Accordingly, the symbol "+/-" will not be displayed unlessthe override takes place, and symbols F and SS are displayed on thedisplay device LDP.

Next, a decision is made to find whether the charge completion signal isbeing input. If the charge completion signal is input from the flashdevice FL to the microcomputer MCB, both the exposure time (content ofthe register TVR2) and the aperture value (content of the register AVR2)for the flash photography are serially transferred to the displaysection DPC, but if it is not input, both the exposure time (content ofthe register TVR1) and the aperture value (content of the register AVR1)for the photography under the ambient light are serially transferred tothe display section DPC. Thereafter, the program flow proceeds to step#49 shown in FIG. 11e.

If it is determined at step #40 that the ISD switch ISS is closed, step#43 takes place at which a "High" is produced from terminal O2. At step#50, a decision is made in order to determine whether the up-shiftswitch UPS is closed or not. When the up-shift switch UPS is closed, adecision is further made at the subsequent step #58 in order todetermine if a fraction of the ISD data is 1/4. If it is 1/4, 1/2 isadded to 1/4 and the result is placed in the register SVR. But, if it isnot 1/4, 1/4 is added to that data and the result is placed in theregister SVR. Accordingly, the fraction portion becomes 1/4 if it is 0,3/4 if it is 1/4, or 0 if it is 3/4. That is, as hereinbefore described,such compromises as 1/3=1/4, 2/3=3/4 and 0=0 are employed. Then, adecision is made in order to find whether or not the content of theregister SVR2 is greater than the maximum ISO data Svm. If the contentof the register SVR2 is greater than Svm, Svm is set in the registerSVR2, but if it is not, Svm remain unchanged. Thereafter, the programflow proceeds to step #52.

When, at step #50, it is determined that the up-shift switch UPS is notclosed, the program flow proceeds to steps #53 and #54 at which onlyterminal O3 is "High". At the subsequent step #55, a decision is made inorder to find whether or not the down-shift switch DOS is closed. Whenthe down-shift switch DOS is closed, and if a fraction portion of themanually present data is 3/4, 1/2 is subtracted, but when it is not 3/4,1/4 is subtracted. In other words, it is assumed as 1/4 if the fractionportion is 1/4, 0 if it is 1/4, or 3/4 if it is 0. Then, a decision ismade in order to determine if the content of the register SVR is smallerthan the minimum ISO data Svo. If the content of the register SVR issmaller than the data Svo, the data Svo is set in the register SVR2, butif it is not, the content of the register SVR remains unchanged.Thereafter, the program flow proceeds to step #52.

In addition, if the result of the decision at step #55 shows that thedown-shift switch DOS is not closed, the content of the register SVRremain unchanged and the program flow proceeds to step #52.

At step #52, flag DCF2 is set to "1", and at the same time, bit MDR0 isset to "1" and bits MDR1, MDR4 and MDR7 are set to be "0". Then, thecontents of the register SVR are loaded in the register IOR, and "High"is produced from terminal O30, thereby carrying out the serial input andoutput operation. Thereupon, a newly presented ISO data is fixedlystored in the storage-register LAC (FIG. 5) within the circuit CIM.Subsequently, data necessary to turn off the display section and the ISOdata are fed to the display circuit DPC and the program flow thenproceeds to step #49.

If at step #41 it is determined that the flag ORF is "1" and theoverride switch ORS is closed, step #44 takes place. That is, at step#57, a decision is made in order to find whether or not the up-shiftswitch UPS is closed. If the up-shift switch UPS is closed, bits MDR2and MDR3 produce "01", and 1/2 is added to the content of the registerORR1. Then, another decision is made in order to determine whether ornot the content of the register ORR1 is above the maximum value ODm. Ifit is above the maximum value ODm, ODm is set in the register ORR1, butif it is not, the content of the register ORR1 is unchanged and theprogram flow proceeds to step #58 at which the flag DCF is set to "1".Then, the program proceeds to step #60.

If at step #57 it is determined that the up-shift switch UPS is notclosed, step #61 takes place to produce "High" from only terminal O3.Then, the program proceeds to step #62 at which a decision is made inorder to determine if the down-shift switch DOS is closed. If thedown-shift switch DOS is closed, 1/2 is added to the contents of theregister ORR2 and, if the result exceeds the maximum value ODm, themaximum value ODm is set in the register ORR2, but if it does not exceedthe maximum value, the content remains unchanged and the flag DCF2 isset to "1". Then, the program proceeds to step #60.

If at step #62 the down-shift switch DOS is not closed, the flag DCF2 isset to "1" without altering MDR2, MDR3 and the registers ORR1 and ORR2,and thereafter, the program goes to step #60 shown in FIG. 11f. At step#60, a decision is made in order to determine if the bits MDR2 and MDR3of the register MDR are "00". If they are "00", they are changed to "11"for the display. Then, MDR0, MDR1, MDR4, MDR7 are made to be "0".Accordingly, in such case, only the symbol "+/-" for the override isdisplayed.

Then, the blank data BLD is output to the register IOR and thentransferred to the display section DPC to turn off the display of digitsindicative of the ISO or SS value. Thereafter, if the contents of MDR2and MDR3 are "01" indicating that the override is effected on the "+"side, the content of the register ORR1 is transferred to the displaysection DPC, but if they are not "01", the content of the register ORR2is transferred to the display section DPC. Then, the program goes tostep #49. At step #49, the content of the register MDR is transferred tothe display section DPC. Then, the terminal 011 is "High", therebyenabling the display by the light emitting diode FLD in the displaysection.

Subsequently, a decision is made to determine if either one of the flagsDCF1 and DCF2 is "1". If either one is "1", it indicates that the datahas been changed. In that case, in order to prevent the data from beingchanged at a high speed, a predetermined time lapses, and then theprogram proceeds to step #65. However, if both of the flags DCF1 andDCF2 are "0", step #65 is carried out immediately. At step #65, theterminals O2, O3 and O4 are "High". Then, it is detected whether or notthe terminals i1, i2 or i3 are "High", that is, whether or not at leastone of the key switches is closed, is determined. If any one of the keyswitches is closed, a data representing five seconds is set in aninternal counter ICO. Then a decision is made to determine if the mainswitch BMS is closed. If the main switch BMS is closed, the terminals O2and O4 are "Low" and a decision is then made to determine if the switchISS has been closed. If the switch ISS is closed, the flag ISF is set to"1", and at the same time, the flags ORF and LMF are set to "0". Then,the program returns to step #41. However, if the switch ISS has not yetbeen closed, a decision is further made as to determine if the switchORS is closed. When it is determined that the switch ORS is closed, theflag ORF is set to "1", and at the same time, the flags LMF and ISF areset to "0". Then, the program returns to step #14. Where both of theswitch ISS and ORS are opened, the flag LMF is set to "1" and theprogram flow then returns to step #14. Accordingly, during a period offive seconds in which none of the switches is closed, the exposure timeand the aperture values are displayed.

If none of the key switches is closed, a decision is made as todetermine if the content of the internal counter ICO is "0". If it is"0", the program flow proceeds to step #67, but if it is not "0", adecision is then further made as to find if the reset switch S4 isclosed. If the reset switch S4 is not closed, the state of the mainswitch BMS is determined. The program then returns from step #66 to step#14.

After the lapse of five seconds subsequent to the opening of all of thekey switches, or at the moment when the reset switch S4 is closed orwhen the main switch BMS is opened, the program goes to step #67,thereby producing a "LOW" from the terminals O1 and O5 to O18, and alsothen, the flags CCF, LMF, ISF and ORF are set to "0", and in turn theinterruption by means of the terminal itA or itB is enabled. And theprogram advances to turn off the display in a manner similar to theoperation at step #3 et seq. Then, the "HALT" condition is established.

When the release switch S2 is closed while the calculation of theexposure control value has been completed to set "1" in the flag CCF,interruption to terminal itA is accepted, and thereafter, the programproceeds to step #70. At step #70, terminal O9 produces a "High" and thepulse of 50 microseconds in duration is output from terminal O8 topermit the data to be read from the flash device. A decision is thenmade to determine if the charge completion signal is input. If it isinput, the content of a register PVR2 in which the value of the numberof f-stop positions to be stopped down for the flash photography is set,is transferred to the aperture control circuit APC. But if it is notinput, the content of a register PVR1 in which the value of the numberof f-stop positions to be stopped down for the photography under theambient light is set, is transferred to the aperture control circuitAPC. Thereafter, a decision is made to determine again if the chargecompletion signal is input. If it is input, the content of the registerTVR2 in which the exposure time for the flash photography is set, istransferred to the exposure time control circuit TIC. But if it is notinput, the content of the register TVR1 in which the exposure time forthe photography under the ambient light is set, is transferred to theexposure time control circuit TIC.

Then, when the terminal O9 is "High", a pulse of 50 microsecond induration is transmitted from the terminal O8 to the flash device FL.Accordingly, the flash device can detect that the exposure controloperation has been initiated. Thereupon, terminal O11 is "Low" to turnoff the light emitting diode FLD so that no lighting display will takeplace during the exposure control. Subsequently, a pulse is output fromterminal O12 to cause the release circuit RLC to effect a shutterrelease operation thereby to initiate the exposure control operation.Then, time lapses until the reset switch S4 closes in response to thecompletion of opening of the shutter curtain, which is effected afterthe completion of the exposure control operation. When the reset switchS4 is so closed, the terminals O2 to O4 is "High". Then, the programreturns to step #67, thereby to repeat the previously describedoperation before the "HALT" condition is established.

FIG. 12 illustrates the details of the display circuit shown in FIG. 4.In this circuit, when a terminal CDP becomes "High", a latch pulse isoutput from a latch control circuit LAC to terminals LN1, LN2 and LN3each time eight synchronizing clock pulses SCP are input. The data readin the serial input register SIR are sequentially taken in registersREG1, REG2 and REG3. Accordingly, the exposure time or the ISO valuedata is stored in the register REG1, the aperture value or the overridevalue data is stored in the register REG2, and the display mode data(that is, the content of the internal register MDR of the microcomputerMCB) is stored in the register REG3. Here, the outputs of terminals e0to e7 correspond respectively to the bits MDRO to MDR7 of the registerMDR.

A decoder DE1 serves to convert the output of the register REF1 into avalue for the display of the exposure time, and a decoder DE2 serves toconvert into a value for the display of the ISO data. A data selectorDS1 serves to send data from the decoder DE1 if terminal e1 is "High",that is, during the exposure time display mode, and to send data fromthe decoder DE2 if terminal e1 is "Low", that is, during the ISO displaymode. In addition thereto, a decoder DE3 serves to convert the output ofthe register REG3 into a value for the display of the aperture value,and a decoder DE4 serves to convert into a value for the display of theoverride. Another data selector DS2 serves to send data from the decoderDE3 if terminal e4 is "High", that is, during the aperture value displaymode, but it serves to send data from the decoder DE4 if terminal e4 is"Low", that is, when the mode is not the aperture value display mode. Afurther decoder DE5 is a decoder operable to convert data for thedisplay of the symbol, based on data from the terminals e0 to e4 of theregister REG3.

A timing signal output circuit TIC serves to output clock pulses of 8 Hzfrom a terminal j1 and clock pulses of 2 Hz from a terminal j2 and alsoto supply a timing signal both to a common signal output circuit COD anda segment signal output circuit SED. The segment signal output circuitSED serves to output a signal for the display, based on the data fedfrom the data selectors DS1 and DS2 and the decoder DE5, to activate aliquid crystal display. If terminal e7 of the register REG3 is "High", 2Hz clock pulses emerge from an AND circuit G1 to cause the liquidcrystal display to blink at 2 Hz.

Both signals from the terminals e5 and e6 of the register REG3 and the 8Hz and 2 Hz clock pulses from the respective terminals j1 and j2 aresupplied to a drive circuit LDC. If a terminal DPE is "High", circuitLDC produces a drive signal to terminal FLD depending on the state ofthe flash device.

FIG. 13 illustrates a flow chart which is a modification of the flowchart shown in FIG. 7. The program flow to step #4 shown in FIG. 13 isthe same as in FIG. 7 except that a predetermined time is allowed topass before the data are completely read out from the film cartridge,and that both the exposure control data and the signal from the filmcounter switch are set in the read-out register MOR. The reason for thepassage of the predetermined time allowed before the data are completelyread out from the film cartridge is because, when the battery is loaded,vibration takes place to such an extent as to result in that the contactof the feelers with the film cartridge may not be stabilized and,therefore, there is the possibility that, if the data are read out fromthe film cartridge immediately after the loading of the battery, theywould be read out erroneously. The predetermined time allowed to passsubsequent to the loading of the battery is so selected for the contactof the feelers with the film cartridge to be stabilized before the dataare actually read out from the film cartridge. When it is determined atstep #4 that the data has been read in from the film cartridge, the dataso read out is set in the register SVR at step #7 and a program flowsimilar to that occurring when the back-up battery BUB is normal and theoutput of the register LAC is also normal is subsequently performed.This will not constitute an exposure error even if the ISO data are readin from the film cartridge at the time of the replacement of thebattery, and neither the blinker display warning of the ISO data nor therelease lock condition takes place.

However, if it is determined at step #4 that no data is read in from thefilm cartridge, the fixed ISO data (ISO 100 Svn) is set in the registerSVR at step #80 and this data is displayed by blinking for ten seconds.If at this time two bits of the register MOR indicates that the counterswitch CFS has not been closed, this ten seconds is utilized as a periodin which no drive is effected by any switch other than the ISO switchISS. Where the counter switch CFS is opened, since the possibility issmall that the film is loaded, only the blinking of ISO is effected andno drive is effected even by S1 and ORS. Unless the ISO switch ISS isclosed, the microcomputer MCB, after the passage of ten seconds,proceeds to step #81 at which the ISO display is effected and thecondition is established wherein a drive can be effected by any switch,the microcomputer MCB being subsequently brought to a halt.

It is to be noted that, in the foregoing embodiment, switch SFC in FIG.4a may be alternatively switched by detecting whether or not the film isactually loaded in the camera, e.g., by detecting the loading of thefilm cartridge or detecting directly the existance of the film (forexample, at a film spool). In such a case the release lock condition canbe disabled by detecting by means of switch SFC that the film has notyet been loaded.

FIG. 14 illustrates an example of the display according to the preferredembodiment of the present invention, wherein FIG. 14a illustrates anexample of the display effected after the setting of the exposure timeand FIG. 14b illustrates an example of the display effected at the timeof the setting of the film sensitivity. As shown in FIG. 14a, the firstdisplay area which is used to display the shutter speed and the filmsensitivity one at a time is shown as displaying the shutter speedreading 1/2000 second, while a second display area is shown asdisplaying another data relating to exposure, e.g., the aperture valuereading F5. 6. However, in FIG. 14b, the first display area is shown asdisplaying the film sensitivity reading ISO 400 while the second displayarea displays nothing. Thus, information to be displayed at the time ofthe setting of the shutter speed is enriched with another data displayedas well as the shutter speed. However, at the time of the setting of thefilm sensitivity which solely depends on an actually loaded particularfilm without any comparison with another data and which has no necessityto be changed depending on each shot as long as the once loaded film iscontinued to be used, nothing is displayed other than the filmsensitivity to clarify such a nature of the film speed setting.

Although in the foregoing embodiment the data on the film cartridge areread out at a particular time after a lapse of a predetermined timeperiod from the closure of the back lid, the concept of the presentinvention can be equally applicable to a type of camera wherein, with nostorage for storing the read ISO information used therein, the ISO datais continuously read in at all times. In such a case, the reading of thedata from the film cartridge is inhibited until the predetermined timeperiod passes subsequent to the closure of the back lid.

In addition, although the switching of the exposure control modes hasbeen described as effected by means of the slide switch, it is to benoted that the same can be effected by a combination of a key forinstructing the change in the exposure control mode and one of theup-shift and down-shift keys. In such a case, it should be designedthat, even by a depression of the exposure control mode changeinstructing key, interruption can be effected to the interruptingterminal itA of the microcomputer to permit the light measurement anddisplay to be performed.

Moreover, although in the foregoing embodiment the back-up battery andthe storage circuit have been described as used for keeping the ISO datastored even when the main battery is removed for replacement purpose,they may not be always necessary. In the case of a camera without such aback-up means, the decision to make both the warning and the releaselock should be effected, depending on whether or not the data issuccessfully read from the film cartridge upon the loading of the newmain battery.

Although the present invention has been fully described with referenceto several preferred embodiments, many modifications and variationsthereof will now be apparent to those skilled in the art, and the scopeof the present invention is therefore to be limited not by the detailsof the preferred embodiments described above, but only by the terms ofappended claims.

                  TABLE 1                                                         ______________________________________                                        ISO       Sv     K2 K3    K4  K5     K6                                       ______________________________________                                         25       3       X       X   X          X                                     32       31/3   X        X   X      X                                         40       32/3   X        X   X                                                50       4               X   X          X                                     64       41/3            X   X      X                                         80       42/3            X   X                                               100       5      X            X          X                                    125       51/3   X            X      X                                        160       52/3   X            X                                               200       6                   X          X                                    250       61/3                X      X                                        320       62/3                X                                               400       7      X        X              X                                    500       71/3   X        X          X                                        640       72/3   X        X                                                   800       8               X              X                                    1000      81/3            X          X                                        1250      82/3            X                                                   1600      9      X                       X                                    2000      91/3   X                   X                                        2500      92/3   X                                                            3200      10                             X                                    4000      101/3                      X                                        5000      102/3                                                                                .        .   .      .   .                                                     .        .   .      .   .                                                     .        .   .      .   .                                                     1        2   4      1/3 2/3                                  ______________________________________                                         : Conductive                                                                  X: Nonconductive                                                         

                  TABLE 2                                                         ______________________________________                                        Register                                                                              Contents               Symbol                                         ______________________________________                                        TVR1    Exposure time for photo-taking                                                                       Tva                                            TVR2    Exposure time for flash photography                                                                  Tvf                                            TVR3    Preset Exposure time   Tvs                                            AVR1    Aperture value for photo-taking                                                                      Ava                                            AVR2    Aperture value for flash photography                                                                 Avf                                            AVR3    Preset Aperture value  Avs                                            ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________    Bit   CAR7                                                                              CAR6                                                                              CAR5                                                                              CAR4                                                                              CAR3                                                                              CAR2                                                                              CAR1                                                                              CAR0                                        __________________________________________________________________________    Position  K12 K11 K6  K5  K4  K3  K2                                          Weight            2/3 1/3 4   2   1                                           __________________________________________________________________________

                  TABLE 4                                                         ______________________________________                                        Bit     Signal    Conditions                                                  ______________________________________                                        MDR0     0        No display of SS & ISO                                               1        Display SS or ISO                                           MDR1     0        Display ISO                                                          1        Display SS                                                  MDR2    01        Override on + side                                          MDR3    10        Override on - side                                                  11        Override 0                                                          00        No display of Override                                      MDR4     0        No display of F-stop                                                 1        Display F-stop                                              MDR5    00        Light off indicating unloading                              MDR6    01        2Hz blinking indicating loading                                     10        Light on indicating charge completion                               11        8Hz blinking indicating FDC                                 MDR7     0        Light on                                                             1        2Hz blinking                                                ______________________________________                                    

We claim:
 1. A camera, comprising:a circuit means; main power sourcemeans for supplying electric power to said circuit means; back-up powersource means for supplying electric power to said circuit meansindependently of said main power source means; means for detectingwhether or not said back-up power source means can supply sufficientelectric power to said circuit means to produce a warning signal whendetecting that said back-up power source means can not supply sufficientelectric power to said circuit means; means for producing a warning inaccordance with the warning signal; means for starting the operation ofthe detecting means when said main power source means is recovered;means for setting data to said circuit means in accordance with a manualoperation; and means for interrupting the operation of said warningproducing means when said data setting means is operated.
 2. A camera asclaimed in claim 1, further comprising means for interupting exposureoperation of the camera in accordance with the warning signal withoperation of a shutter release member of the camera.